Ask Mr. Smarty Plants

First, something we frequently have to repeat: The Lady Bird Johnson Wildflower Center is dedicated to the growth, propagation and protection of plants native not only to North America but also to the area in which is is being grown. This USDA Plant Profile Map shows that Muhlenbergia dumosa is native only to Arizona; however our Native Plant Database does not list it at all. We did find an article on this plant from Austin Native Landscaping on Muhlenbergia dumosa, Bamboo Muhly, Fauny Bamboo, which includes this line:

"Texas Native: No, but particularly well adapted to central Texas and Austin."

Beyond that, we will have to give you some other information on toxicity to horses, and then help you find some appropriate perennials for this area, leaving the detective work up to you, checking lists of things horses might destroy or that might destroy the horse against your resulting lists of plant possibilities.

Previous answer on plants toxic to horses.

From About.com What Horses Eat

To help you learn to use our Native Plant Database, we will choose a small selection of shrubs and herbs (herbaceous blooming plants) for either shade (2 hours or less of sun a day) or sun (6 hours or more of sun). You can follow each plant link to our webpage on that plant to learn its growing conditions, means of propagation, etc. The best list we have for this is found by going to our Recommended Species section, click on Central Texas on the map and you will get this list of 157 plants native to Central Texas. Using the selection list on the left hand side of that page, we will first choose "shrub" for Habit, "perennial" for Duration and make 3 selections with"sun" selected under Light Requirements. Repeating the search for "shrub," on "shade" we will choose 3 more shrubs. Then, we will repeat the process, selecting "herbs" (herbaceous blooming plants) for Habit. You can then tweak your selections however you wish, for other Habits, Light Requiremnts, height, bloom time and/or color, even evergreen or deciduous. Of course, the more characteristics you choose, the fewer selections will fit all of them, up to and including none.

Shrubs for Sun for Central Texas:

Chrysactinia mexicana (Damianita)

Leucophyllum frutescens (Cenizo)

Sophora secundiflora (Texas mountain laurel)

Shrubs for Shade for Central Texas

Ilex vomitoria (Yaupon)

Malvaviscus arboreus var. drummondii (Turk's cap or turkscap)

Salvia regla (Mountain sage)

Perennial Herbaceous Blooming Plants for Sun in Central Texas:

Conoclinium coelestinum (Blue mistflower)

Echinacea purpurea (Eastern purple coneflower)

Lobelia cardinalis (Cardinal flower)

Perennial Herbaceous Blooming Plants for Shade in Central Texas:

Aquilegia canadensis (Eastern red columbine)

Coreopsis lanceolata (Lanceleaf coreopsis)

Salvia coccinea (Scarlet sage)